The molecular identification of SARS-CoV as the virus causing the clinical SARS disease opens many avenues for studies of disease pathogenesis, prevention and treatment. The pulmonary tract is likely the major portal of entry for this virus and disease of the lung is a significant source of SARS-associated morbidity and mortality. We hypothesize that the airway epithelial surface is the initial point of contact between the host and the SARS-CoV. Currently little is known regarding the host-pathogen interactions at this critical mucosal interface for this infection. The overall goal of this project is to understand how SARS-CoV enters polarized human airway epithelia and other lung cell types and to identify epithelial innate host defense responses that are elicited in response to the pathogen that may influence disease pathogenesis. We will also investigate how this knowledge may be applied towards the development of treatment or prevention strategies for SARS-CoV pulmonary infections using RNA interference (RNAi) technology. There are three specific aims: Aim 1. What is the route of entry and exit for SARS-CoV in human airway epithelia? We will use well-differentiated primary cultures of human airway epithelia to investigate several aspects on SARS-CoV entry and exit from this important target cell. Aim 2. What is the relationship between SARS-CoV and interferon-dependent epithelial immunity? The following questions will be addressed: Does SARS-CoV infection induce interferon release from respiratory epithelial cells? Do interferons inhibit SARS-CoV replication in respiratory epithelial cells? How does SARS-CoV infection subvert interferon-dependent immunity? Aim 3. Can mucosal immunity to SARS-CoV be enhanced through use of RNA interference? RNA interference is a powerful method to selectively target mRNA degradation in mammalian cells. We will evaluate the use of RNAi as a specific method to inhibit viral infection and replication in human airway epithelia. Completion of these studies will provide a wealth of new information and insight regarding the interactions between the pathogenic coronavirus and the epithelial cells of the human lung.